Hi Laura,
I also have frizzy (More wavy than curly) hair that, yes, is in a ponytail at the moment! I live in a high humidity state,Georgia, and the only thing I can do in the summer is grin and bear it. Well, not so much grin, but I accept it as a temporary condition.
Like others have said, you really need to think about the grow in process bc you will have to either maintain it for a long while or deal with the regrowth. (Like relaxers, a lot of the breakage after chemical services occurs at the point where the straightened and curly hair meet). Since you have long hair, it really could take over a year to get back to curly if you decide to.
Two friends who have done the thermal straightening have no frizz but the hair holds no curl at all. Time between touch-ups depends on how coarse your hair is & how well you can straighten it with blow dryer. I think 1 was able to wait 4-6 months before having to re-do treatment.
My husband is a stylist and we sell beauty products at our salon, so like you I have tried EVERY product out there. I have found that there is NO one miracle product but a 5 step process for keeping the frizz under control. 1. Moisturizing Shampoo & Conditoner 2. Hair serum (on wet hair) to seal hair cuticles 3. Leave-in conditioner or mousse for moisture 4. Styling gel for hold 5. Comb thru,air dry and do not touch hair until completely dry (Yes, takes forever in summer!)
Ok, after all that hair MAY stay frizz free until either you start sweating or until lunchtime, which ever comes first!
Only 8 frizzy weeks until September...